The present invention relates to steering-bearing assemblies for bicycles, of the type comprising:
a head tube, which forms part of the frame of a bicycle;
a steering tube, for connecting the front fork of a bicycle to the handlebars of the bicycle;
a bearing assembly, for supporting the steering tube so that it can turn within the head tube, in which said bearing assembly includes:
an upper bearing unit; and
a lower bearing unit;
in which said lower bearing unit comprises:
a first race connected to said head tube;
a second race connected to said steering tube; and
a bottom supporting ring arranged between said second race and the steering tube and having a bottom face substantially perpendicular to the axis of the assembly that rests against a stop surface of the fork.
A steering bearing assembly of the type referred to above is, for example, described and illustrated in U.S. Pat. No. 5,893,574 assigned to the present applicant.
In the said known device, which has also been produced and marketed by the applicant, the aforesaid bottom supporting ring, which rests against the stop surface of the fork, is rigidly connected to the steering tube by means of an interference fit. A possible disassembly of the aforesaid bottom supporting ring is usually obtained by introducing a tool between the undersurface of the bottom supporting ring and the stop surface of the fork so as to exert on the bottom supporting ring a force which tends to move it away from the aforesaid stop surface. More recently, however, there has been a wide diffusion of steering bearing assemblies in which the first race of the bottom bearing assembly rests directly against the inner surface of the head tube, and the latter has a lower end portion that extends downwards until it is adjacent with the aforesaid stop surface of the fork, surrounding the bottom supporting ring completely. In such structures, disassembly of the bottom supporting ring, which is previously mounted with interference fit, consequently proves problematical, in so far as access of a tool to the undersurface of the bottom supporting ring proves difficult, and in so far as it is moreover difficult to exert on the bottom supporting ring a sufficiently large force to enable its disassembly.
The purpose of the present invention is to provide a steering bearing assembly of the type referred to at the beginning of the present description in which the aforesaid bottom supporting ring can be mounted and removed with extreme ease and speed.
With a view to achieving the above purpose, the subject of the invention is a steering bearing assembly having all the characteristics indicated at the beginning of the present description and further characterized in that the aforesaid bottom supporting ring is mounted with play on said steering tube. Preferably, the aforesaid bottom supporting ring incorporates elastic means which recall it towards a configuration of minimum diameter in order to keep said bottom supporting ring blocked on said steering tube. Thanks to this characteristic, the bottom supporting ring forming part of the steering bearing assembly according to the invention can be mounted with extreme ease at the base of the steering tube, exploiting, if need be, the elasticity that the said bottom supporting ring possibly has. In the same way, the operation of disassembly proves extremely easy as compared to the case of disassembly of a ring mounted with interference fit as in the known solutions.
Preferably, the aforesaid bottom supporting ring is made of plastic material. In this case, according to the preferred embodiment of the invention, the bottom supporting ring is made up of a plurality of ring sectors which are identical and separate from one another and around which an open-ring wire spring is set. This conformation and arrangement enables a more standardized and economical fabrication of the supporting ring made of plastic material.